Dynamically balanced thermal relay



Mud! 1940- c. M. HATHAWAY 2,195,304

DYNAMICALLY BALANCED THERMAL RELAY Filed July 9, 1958 Inventor- Claude M Hathaway, y E fin v5 J His A torney.

Patented Mar. 26, 1940 UNITED STATES 2,195,304 I DYNAMICALLY naumcsn 'rnnamn may Claude M. Hathaway, Nlskayuna, N. Y., assignor to General Electric Company, a corporation of New York Application July 9, 1938, Serial No. 218,477

13 Claims.

My invention relates to thermal relays and more particularly to an improved thermal relay ior use in those installations where the relay in operation is subjected to extreme conditions of mechanical vibration. While not limited thereto, my invention is particularly suited for use in controlling the temperature of a piezoelectric device such as may be used with signalling equipment provided in aircraft.

l0 Occasions frequently occur where it is desirable that the temperature of an enclosed space be maintained within predetermined temperature limits. The temperature responsive relay is admirably suited to accomplish this result by virtue of the fact that it has a relatively high sensitivity combined with a fairly rugged and rather simple :onstruction. The delicate balance of forces which govern the operation of a relay of this type as it functions to control a source of heat energy 1) has, heretofore, dictated an outstanding limitation to its use in that the relay could not be used under those conditions where, during its operation, it would be subjected to mechanical shock and vibration. Such shock and vibration 35 upsets thedelicate balance of forces acting in the relay to create an erroneous operation leading to erratic results. This is particularly objectionable in certain types of service to which the relay would otherwise be adaptable as, for example, in installations or radio apparatus in mobile craft where the limitation here considered leads not only to an impaired temperature control by the relay, but additionally results in a greatly reduced life of the relay through the burning of 35 the electrical contacts with which it is provided and in the creation of an unduly large amount of interference, through the chattering of the relay contacts, with the proper functioning of radio receiving apparatusoperating in the immediate 4o neighborhood.

It is an object of my invention to provide a thermally responsive relay whose operation is substantially unaffected by extreme conditions of mechanical shock and vibration.

45 A further object of my invention is to provide a thermal relay wherein magnetic elements are provided to magnetically and electrically damp vibrational movements of the relay elements while aiding the normal temperature responsive move- 50 ments of the relay elements by eflecting a snapaction of the elements to their circuit controlling positions.

The novel features which I believe to be characteristic of my invention are set forth with par- 55 ticularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawa ing in which the single figure represents in elevational view a thermal relay which embodies my invention.

Referring to the single figure of the drawing, each of a pair of bimetallic thermal responsive members it is fixedly secured at one end in cantilever fashion to a yieldable member II which in turn is supported from a base member I2 of insulating material by a bracket l3. The secured end of the bimetallic member Ill may be 16 positioned in a plurality of selectable positions with respect to the base member l2 by a threaded screw member it which screws through a threaded aperture, not shown, in the bracket H. A lock nut l5 secures the threaded member M in 20 adjusted position against the force exerted by the yieldable member II. The purpose in providing the threaded member It will be explained more fully hereinafter.

A permanent magnet I 6, preferably of a material having relatively high residual magnetism combined withhigh coercive force, as, the well known material called alnico, is supported in spaced relation to the free ends of the bimetallic members III by a bracket H. The poles [8 of the 80 magnet I6 are adjustably spaced from opposing magnetizable iron members l9, which are secured upon the free ends of the bimetallic members III, by the provision of securing slots 20 provided'in the supporting bracket ll.

In addition to the magnetizable members l9, each of the bimetallic members ID has secured near its free end a hollow cylindrical magnetizable iron sleeve 2| in the center of which, and projecting beyond the end of the sleeve, is a silver 40 contact 22. A sheet of material 23 having good electrical current conductivity, as copper or the like, is secured to the upper surface of each magnetizable member IS in opposing relation to a corresponding pole [8 of the magnet Hi. The purpose in providing the material 23 will be presently explained.

It will be understood that the bimetallic members Ill respond to temperature changes by unequal expansions or contractions of the dissimilar m metals which comprise these members with a resultant bending of the member and relative movement of the free end of each. The members III are so arranged that increasing values of temperature, or decreasing values as desired, result 56 in movement 01 the iree ends of the bimetallic elements in opposite directions to separate the contacts 22. It will further be understood that a thermal relay as thus constructed may be used to control a source of heat energy by controlling an electrical circuit in which the relay contacts are connected. The controlled electrical circuit is completed through the relay from one of the brackets l3, through a corr sponding yieldable member ii and bimetallic member it, and through a contact 22in the cor responding contact and the other bimetallic ele ment l0 and therethrough to the other bracket l The upper temperature limit at which the contacts 22 separate threaded member i not shown, provided in the bracket is adjusted by adjusting the d in the threaded aperture, $3. The

threaded member is loclzed, as previously BE" plained, in adjusted position by the loclmut The bimetallic mern ers iii are substantia t duplicates both in the dimensions and materials of their construction and in the method oi? supporting tl'lem from the base it. Similarly. the elements 22 and 23, which are secured to the free end of each bimetallic member have substantial identity of material, form, and Weight. Since, therefore, the bimetallic members it are of similar mass and stiffness and are similarly loaded, a relay constructed according to my invention is inherently insensitive to external vib 'atory forces to which the relay may be subjected. That is. the bimetallic members Hi have at a given instant equal vibrational accelerating forces applied thereto but the members to are of equal stiffness and are equally loaded and therefore move together in the same direction under the influence of the vibrational forces. 'l'hus if the relay contacts 22 are in engagin relation at a particular moment during the operation of "the relay, mechanical vibration of the relay has no tendency to open the relay contacts. Likewise, if the contacts 22 at a particular time are separated, vibration of the relay does not cause the contacts to reengage.

Rapid movement of the free end of the bimetallic member id, as would be caused by mechanical vibration or shock of the relay, is eiiectivcly damped by the eddy currents which are induced in the finest of current conducting material 23 as this material moves through the magnetic flu}; which extends between a pole l8 of the magnet to and a corresponding magnetizable member ii]. The magnitude of the eddy currents thus produced, and therefore the magnitude of the damping action, increases in proportion to increasing values of velocity of the moving material Eddy currents are similarly produced in the magnetizable member 59 as this member is displaced along the face of a respective magne pole l0 by the movement of the bimetallic member Additionally, the displacement of the magnetizable member l?) with respect to a cor-= respond ng magnet pole i3 results in a force which tends retard or damp the movemer'- of magnetizable member by virtue of v :esis losses in this member through cha All of e r e retarding or clamhere considered forces e., the damping 1 reduced the several currents and My hysteresis losses) exert influence tending restrain movements of the bimetallic mero- Ler be": e conducting mate 15L and thus effectively and quickly damp any movement of the bimetallic member which may result from mechanical vibration of the relay.

It will be evident that the damping forces previously considered are aided by the frictional forces existing between the contacts 22 whenever the contacts are in engaging relation and being thus engaged are displaced relative to one another by movement of the bimetallic members ill while moving together in the same direction.

A thermal relay constructed according to my invention the additional advantage oi. a snap-action t me of operation. That is, as the contacts '22 separate due to bending of the bimetallic mbers t3, r between the mag:- netizabie sleeves 2i increased thereby decreasing magn tic force of attraction between in magnetic force an the increase of the bimetallic inc-1n hers e of changing values of tem zerature with u .e result that contacts '22 rag move apart to ir separated posi tions the upper temperature limit is reached. its the temperature drops and the bimetallic members ill bend toward each other, the magnetis force of attraction between the magnetizable sleeves it increases at a more rapid rate than the decrease of the force which maintains the bimetallic members it bent position. Thus as the contacts 22 approach each other, a point is reached at which the contacts move rapidly togather into contact. The spacing between the poles l8 oi. the magnet l5 and the magnetizable members it may be adjusted to adjust the degree of snap-action thus provided.

It will now be evident from the above description that my invention provides a temperature responsive relay of the snap-action type which is both dynamically balanced and damped to such a high degree that it may be used under extreme conditions of mechanical vibration even where those conditions are as severe as are commonly encountered in the temperature control of piece-electric devices provided in radio communication equipment in airplanes.

While I have shown a particular embodiment of my invention, it will, of course, be understood that I do not wish to be limited thereto since many different modifications may be made in the arrangement of the elements of the apparatus described. I, of course, contemplate by the amended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What claim as new and desire to secure by Letters latent of the United States, is:

l. in a thermal responsive relay, the combination enpansihle movably responsive to temperature variations controlling an operation, means for rendering said first-named means substantially un esponsive to mechanical vibrations to which "l relay is subjected, said "a a current conducta expansible means, a magnetic field of motion of said atlonal movements electrically verse to said field. thermal responsi e ponse changes trical circuit conour said rstperimttlng;

vibrational movements of said first-named means under the influence of external vibrational forces to which said relay is subjected, and means for electrically damping said vibrational movements of said first-named means, said last named means comprising a current conducting member movable by said first means, and means for establishing a magnetic field transverse to the direction of motion of said member, whereby rapid vibrational movements 01' said first means are electrically damped by motion of said member transverse to said field.

3. The combination, in a temperature responsive device, of means movably responsive to temperature variations for controlling an electrical circuit, means for dynamically balancing said first-named means to render the operation of 1 said device roughly insensitive to mechanical vibratory forces to which said device is subjected, and means for magnetically damping vibratory movement of said first-named means to render the operation of said device highly insensitive to said mechanical vibratory forces, said last named means comprising a current conducting member movable by said first means and means for establishing a magnetic field transverse to the direction of motion of said member, whereby rapid vibrational movements of said first means are electrically damped by motion of said member transverse to said field.

4. The combination, in a thermal responsive relay, oi expansible means movably responsive to temperature variations for controlling an electrical circuit, said means having a movable portion which vibrates when said relay is subjected to mechanical vibration, means for producing a. magnetic field, electric current conducting means in magnetic fiux intercepting relation to said lastnamed means, and means responsive to move-' ment of said first-named means for producing.

corresponding transverse movement 01 said current conducting means in said field thereby to produce electrical currents which oppose said vibrational movements 01' said first-named means to render the operation of said relay substantially unresponsive to mechanical vibration.

5. A thermal responsive relay comprising, in combination, a base member, a pair of bimetallic thermal responsive members each having an end rigidly secured in a plurality of selectable positions on said base member and having a movable end, means responsive to the movement oi said movable ends in opposite directions for controlling an electrical circuit, magnetic means, magnetizable means spacedfrom and in cooperating relation to said magnetic means, and means for eiiecting relatively rapid movements of said movable endsin opposite directions but relatively slow movements of said movable ends in thesame direction, said last-named means including means to increase the length of the magnetic circuit of said magnetic and magnetizable means upon movement 01' said movable ends away from each other and to produce changes in the magnetization of said magnetizable means by said magnetic means upon movement or said movable ends in the same direction.

6. A thermal responsive relay comprising, in combination, a pair 01' thermal responsive members, means for supporting said members cantilever iashion in spaced-apart relation with a free end of each opposing and movable in the same direction in response to mechanical vibrations and in opposite directions in response to temperature changes, means responsive to the movement of said free ends in opposite directions for controlling an electrical circuit, a magnet, means for supporting said magnet in spaced relation to said free ends, and means secured to and movable with said free ends through the field of said magnet for accelerating the movement of said free ends in opposite directions while opposing the movement of said free ends in the same direction whereby vibratory movements of said free ends are quickly damped.

'7. The combination, in a temperature responsive relay, of a pair of bimetallic thermal responsive members, stationary means for supporting said members cantilever fashion in spaced-apart parallel relation, said last-named means positioning said members with their free ends opposing, means responsive to the movement of said free ends in opposite directions for controlling an electrical circuit, a magnet, means for supporting said magnet adjacent said free ends, and magnetizable means secured to each of said free ends and movable therewith adjacent the pole movement of said free ends in the same direction while providing snap-action motion of said free ends when moving in opposite'directions.

8. In a thermal relay, the combination of a thermal responsive member having a relatively fixed portion and a portion movable under the influence or thermal changes, means responsive to movement .01 said movable portion for controlling an operation, said, relay being subjected during operation'to mechanical vibration which tends to produce undesirable movements of said movable portion, and means for reducing said undesirable movement, said last named means including current conducting means arranged to move with said movable portion, and means for establishing a magnetic field transverse to the movement of said current conducting means, whereby current induced in said current conducting means by motion in said field tends to oppose faces of said magnet for damping the concurrent said motion and damps motion of said movable the eifect on said controlled operation of said undesirable movements, said last named means ineluding means for supporting said members in dynamically balanced relation with each other, means for establishing a magnetic field, and means arranged to move individually with each 01' said movable portions for producing from said magnetic field a force opposing said undesirable movements. l

10. A dynamically balanced thermal relay comprising, in combination, a pair of thermal responsive devices each. having a portion movable in.

response to changes of temperature, each of the movable portions of said devices having substantially the same period or mechanical vibration,

means responsive to the movement ot said movable portions with changes of temperature for controlling an operation, means supporting said devices each in dynamically balanced relation with the other to render the operation of said relay roughly unresponsive to mechanical vibrationtowhlchsaidrelayissubiectedduringoporation, means for producing a magnetic field, and means movable through said magnetic field and responsive to rapid movements of the movable portions of said devices for producing a force opposing said rapid movement whereby the op eration of said relay is rendered highly insensitive to vibrational forces.

11. dynamically balanced thermal relay comprising, in combination, a pair of bimetallic thermal elements each having a portion movable in response to changes of temperature, means for supporting said elements in dynamically balanced relation with said movable portions opposing, means for producing a magnetic field, and means responsive to rapid movement of said movable portions through said magnetic field for producing a force opposing said rapid movement whereby the operation of said relay is rendered unresponsive to external vibrational forces.

12. The combination, in a dynamically balanced thermal relay, of a pair of bimetallic thermal elements, each having the same period of vibration, each of said elements having a portion movable in response to changes of temperature, means for supporting said elements in dynamically balanced relation to each other, means for producing a magnetic field transverse to the direction of movement of said movable portions,

means movable individually with the movable portion of each of said elements for producing with said magnetic field a force opposing rapid vibrational movements or said movable portions, and means movable with at least one of said movable portions for establishing a magnetic path between said movable portions to produce a snap-action operation of said relay.

13. The combination in a thermal responsive device, of a pair of members, each having a fixed portion and a movable portion, said pair of members being so proportioned and placed with respect to each other that shock produces no relative movement between the movable portions of said pair or members, means for producing relative movement between the movable portions of said pair of members upon change in temperature, means responsive to relative movement of said movable portions for controlling an opera tion, current conducting means associated with and movable by each of said movable portions, and means for establishing a magnetic field through which each of said current conducting means moves, whereby current is induced in said current conducting means upon motion of said movable portions so that said motion is rapidly damped.

CLAUDE M. HATHAWAY. 

